Definition of "thermometer"

Towards the following morning, the thermometer fell to 5°; and at daylight, there was not an atom of water to be seen in any direction.

1835, John Ross, James Clark Ross, Narrative of a Second Voyage in Search of a North-west Passage …, Volume 1‎, pages 284–5

The brothers had thrust the thermometer between two circuit boards in order to look for hot spots inside m zero. The thermometer’s dial was marked “Beef Rare—Ham—Beef Med—Pork.” “You want to keep the machine below ‘Pork,’” Gregory remarked.

1992 March 2, Richard Preston, “The Mountains of Pi”, in The New Yorker